The present invention relates to a current measuring device and method. More specifically, the invention relates to a current measuring device and method which measures a current, using a coreless current sensor.
An electrical configuration with a current transformer is used to measure electrical current flowing through a conductor. In this configuration, a magnetic core is used to attract the magnetic flux around the conductor with the current being measured while the conductor is isolated from the current transformer.
However, the current sensor with a magnetic core generates a large amount of heat due to magnetic losses. Furthermore, there are some problems associated with reductions in size, weight and cost.
In order to solve these problems, a current measuring device using a coreless current sensor has been developed. A coreless current sensor measures a current without a magnetic core. As a coreless current sensor, a device (i.e., a hole element) which generates a voltage corresponding to the magnetic-flux density is known.
According to Japanese Unexamined Patent Publication No. 2005-207791, as shown in FIG. 6, four magnetic sensors 22A, 22B, 22C and 22D along with three conductors 21A, 21B and 21C are arranged alternatively at distance r. Each magnetic sensor detects the current flowing through each conductor and outputs a voltage signal corresponding to a magnetic-flux density. Processing part 23 performs a prescribed arithmetic processing for the signals from the magnetic sensors, so that the current flowing through each conductor is obtained. In this case, the influence of external magnetic fields (in other words, magnetic fields which appear according to factors other than the current flowing through the conductors) cancels each other out since the number of the magnetic sensors is greater than that of the conductors.
However, in this configuration, it is difficult to accurately measure the current unless the property of magnetic sensors is uniform, there is equality in the distance r, or external magnetic fields are uniform. Moreover, because the number of magnetic sensors must be greater than that of the conductors, this current measuring device is large in size. In addition, when measuring an alternating current generated by a switching power supply, the noise generated by the switching operation may affect the measurement.